Integral strain transducer



Feb. 26, 1963 R. R. KoolMAN INTEGRAL STRAIN TRANsDUcER Filed Feb. 1Q 1961 6 Sheets-Sheet 1 FIG. 2

ATTORNEYS Feb. l26, 1963 R. R. KOOIMAN INTEGRAL STRAIN TRANSDUCER 6 Sheets-Sheet 2 Filed Feb. l, 1961 FIG. 5

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INVENTOR. ROBERT R. KOOIMAN BY ATTORNEYS Feb. 26, 1963 R. R. KoolMAN INTEGRAL STRAIN TRANSDUCER 6 Sheets-Sheet 3 Filed Feb. 1, 1961 als 255 ala FIG. I I

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INVENTOR. ROBERT R. KOOIMAN BY ,@-wg/MM ATTORNEYS Feb. 26, 1963 R. R. KoolMAN 3,079,576

INTEGRAL STRAIN TRANSDUCER Filed Feb. l, 1961 6 Sheets-Sheet 5 F IG. l5

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ROBERT R. KOOIMAN BY/QWI/y ATTORNEYS Feb. 26, 1963 R. R. KOOIMAN 3,079,576

INTEGRAL STRAIN TRANSDUCER y Filed Feb. l, 1961 6 Sheets-Sheet 6 FIG. 22 4,5

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` INVENTOR. ROBERT R. KOOIMAN ATTORNEYS United States Patent O `,tll9,57t INTEGRAL TRAIN TRANSIIUCER Robert R. Kooiman, Mnneapoiis, Minn., assigner to Rosemount Engineering Company, Minneapolis, Minn., a corporation ot Minnesota Filed Feb. 1, 1961, Ser. No. 86,337 37 Ciaims. (Cl. E38-4) This invention relates to integral strain transducers, and more particularly to devices which are capable of being placed under pressure by a tiuid pressure and of changing thei-r electrical resistance or other electrical characteristics due to such applied iiuid pressure. This application is a continuation-impart of my applications, Ser. Nos. 22,186 and 22,187, both tiled April 14, 1960, both abandoned.

Heretofore strain transducers for providing an electrical signal, as a result of applied pressure, have utilized a pressure responsive Vehicle for imposing a movement upon some separate device such as an electrical resistance, the amount of Which is changed due to such movement. These devices have the disadvantage that they require multiple parts, they frequently require rnotion mult`plying mechanism, and they are not `sutlciently rugged and are expensive to build.

It is an object of the present invention to provide a strain transducer capable of receiving a fluid pressure and of being motiva-ted thereby, and which when so motivated will change its electrical characteristics for producing an electric signal. It is another object of the invent`on to provide a strain transducer and/or system for receiving iluid pressure either interiorly or exteriorly or both, and for providing an electrical sign-al as a result of such pressure. It is another object of the invention to provide an integral strain transducer of rugged construction which can be manufactured at low cost.

It is another obje-ct of the invention to provide integral strain transducer systems capable of use under extremely adverse conditions of temperature, stress, vibrations, etc.

It is another object of the invention to provide integral strain transducers in a variety of coniigurations and wherein the transducer material may be or" metal or semiconductors or treated semi-conductors.

It is another object of the invention to provide integral strain transducers wherein a semi-conductor is utilized and provision is made for providing signals of optimum effect or, where desired, of opposite sign when pressure is applied.

Other and further objects are those inherent in the invention herein illustrated, described and claimed and will be apparent as the description proceeds.

To the accomplishment of the foregoing and related ends this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principles of the invention may be employed.

The mechanism is illustrated with reference to the drawings wherein corresponding numerals refer to the same parts, and in which:

FIGURE l is an isometric View showing a fragment of tube, for illustrative purposes in relation to the theory of the invention;

FIGURE 2 is an isometric view in longitudinal section showing one form of the invention;

FIGURE 3 is an isometric View in longitudinal section of another form of the invention;

FIGURE 4 is a longitudinal sectional view illustratice ing another form of the invention, together with the accompanying circuitry;

FIGURE 5 is a longitudinal sectional View for a moditied form of the invention including the accompanying circuitry;

FIGURE 6 is -a plan elevational view and accompanying diagrammatic view of the circuitry of a modied form of the invention;

FIGURE 7 is a plan view of a modified form of the invention, with the circuitry involved;

FIGURE 8 is a further modified form of the invention shown partially in longitudinal sectional View, together with the circuitry involved;

FIGURE 9 is a further modified form of the invention shown in longitudinal sectional view;

FIGURE l0 is a longitudinal sectional view and circuitry of a modiiied form of integral strain transducer according to the present invention;

FIGURE 1l is a longitudinal sectional view of another modied form of the present invention;

FIGURE 12 is a longitudinal sectional view, together with the circuitry of a further modified form of the present invention;

FIGURE 13 is a longitudinal sectional view of a further rnoditied form of the invention, together with the circuitry;

FIGURE 14 is a longitudinal sectional view of another modied form of the present invention together with the circuitry;

FIGURE 15 is a sectional view of a modified form of the invention utilizing a semi-conductor pressure transducer element having a tired edge support;

FIGURE 16 is a plan view of the device shown in FIGURE 15 as viewed from the direction I6-16 of FIGURE 15;

FIGURE 17 is a transverse sectional View through a modified form of the invention utilizing a treated semiconductor disc;

FIGURE 18 is a plan view of the device shown in FIGURE 17 as viewed from the direction 13 13 of FIGURE 17;

FIGURE 19 is a plan view similar to FIGURE 18, but showing a further illustrative embodiment of the invention;

FIGURE 20 is a sectional view through a further illustrative form of semi-conductor transducer element;

FIGURE 2l is a further illustrative form of the invention utilizing a semi-conductor tube as the vessel;

FIGURE 22 is an isometric view in longitudinal section similar to FIGURE 1 but showing a still further mod ied embodiment of the invention together with the accompanying circuitry;

FIGURE 23 is a cross-sectional view taken along the line and in the direction of the arrows 2222 of FIG- URE 22;

FIGURE 24 is an end view taken along the line and in the direction of the arrows 2li-2a of FIGURE 22;

FIGURE 25 is a plan view similar to FIGURE 19 but showing a still further modified embodiment of the invention;

FIGURE 26 is a longitudinal sectional View similar to FIGURE 13 but of another modified form of the invention;

FIGURE 27 is a plan View of FIGURE 26 taken along the line and in the direction of the arrows 27-27 of FIG- URE 26;

FIGURE 28 is a longitudinal sectional view of a modiied form of integral strain transducer of this invention, and

FIGURE 29 is a fragmentary plan View of FIGURE 27 apresta talfienA along' the'line vand in the direction of" the arrows- The invention, in its simplest form, is a pressure con-k ofv are stressed when fluid pressure isapplied. V'Ihe'stress produced in'the material of which the vessel (or certaine portions of the vessel) is composed causes changes of resistance to occur, which` are indicative of the pressure lchange. i i i y According to the' present invention, the application of pressure internally' or externally of the vessel causes' changes in dimension due to pressure loading, and causes'- ch'anges'in the resistivity of the vessely or portions there- VariousV materials are suitable for use in providing the integral strain transducers of the'present invention'. Pre'- ferred materials are metalalloys such as manganin and an alloy of 42% nickel, 58% iron and various semi-conduct-or elements and compounds such as germanium', silicon', diamond, silicon' carbide, indium antimonide, zinc telluride', gallium phosphide andy rutile'. l

A material such as the alloy,rmanganin, exhibitscharacteristics very favorable lfor use in making the longer tubular and hemispherical coniiguraticn integral strain transducers of the present invention. Manganin, which is illustrative, has a high resistivity and low thermal coeliicient of resistivity. Semi-conducting materials geul erally exhibit much largcrstrain co-eicientsof resistlv# ity than metals; however, their thermal co-eficient of resistivity is also proportionately higher. Semi-conductors, which in general can be fabricated less readily than metals, are best adapted for simpler coniigurations of integral strain' transducers of the invention, such as short tubular, disc, and cup configurations. v

The invention, in its simplest form, can be used to measure a uniform pressure wherein the pressure transduci-ng devicevis a tubularmember, or members, into or upon which a duid pressure is applied.

FIGURE 1 shows a short section of a cylindrical pressure transducing clement of the invention wherein the cylinder is designated i' and has a wall thickness 11. According to the invention, pressure may be applied within the tube It) or the tube may be sealed so that pressure may be applied to the exterior surface of the wall forming the tube. When the material of which the tube is composed is thus subjected to such external or internal pressure, every particle of material within the tube is stressed and undergoes a change in resistivity/. Thus, if one considers a particle 12o-f material withinthetube wall, it is subjected to stresses along three axes as shown in FIGURE l, namely the axis xx, which is parallel to the centerline of the tub'e (or stated anothei way, lengthwise of the tube); along the axis yy, which is tangential to the circle 13, about the centerline, in which the particle 12 is found, and which may be considered as the hoop tension applied to the particle I2, and alo-ng the axis zzwhich is a radialraxis from the centerline CL outwardly through particle V12I d d l l, i Y

rIhis same theory holds true whether the partice of material is a part of a tube as in FIGURES 1-9, or Whether it is a part of a disc, such as in FIGURES lil-20.

Referring to FIGURE 2, the integral strain transducer here illustrated is a cylinder having a plug 2l set in the left end, and a plug 2 2 set in the right end. Both plugs are sealed to the tube. The plug 22 is apertured so as to receive the pipe I3, by means of which a huid pressure may be introduced into the cylinder. The plugs 21 and 22 are soldered or otherwise sealed to the tube 20. Electrical connections via lines 24 and 25 are provided on the ends of tube ZIP; Accordingly', when the tube 2t) has pressure applied to the interior thereof, a change in resistance will-occur as between lines 24 and 25, thereby" providing the signal, indicating the amount of pressure.

Referring to FIGURE 3, in this form of the inventon` the cylinder 39 is provided with solid plugs 31 and 32 at opposite ends, these plugs being sealed by soldering or otherwise sealing to the material forming the wall of the cylinder. The cylinder thus plugged at each end forms an enclosed 'capsule which may be evacuated at time of sealing, and-,it is mounted within a pressuretight'container 35, which is provided with an inlet connection at 36. The lead wires 33 and 34 which are connected to opposite ends of the cylinder 30 are taken out'through the wall of the container35 throughpressure tight insulating bushings33A and 34A.

In this form of he' invention', vpressure is applied' via piped, as shown by arrow 37 and' this fluid pressure is accordingly imposed on all of the exterior surfaces of the cylinder 30 andI of course of the plugs 3i and 32. The cylinderl 3i) is accordingly placed under stress and as' a result its resistance is changed.-

In FIGURE 4 there is' provided a system utilizing a." pair of integral strain transducers according tothe pres-f ent: invention. This pair of transducers comprises'identif cal cylinders, of which the one at the left inFIGU'RE' 4- may be' identical' with the" cylinder 2t? in FIGURE 2;v This cylinder is provided with the plugfZl at one end and the plug 22 at' the' opposite end together with the inlet connection 13 by means of which pressure may be introduced into the interior of the cylinder 20. The companioncylind'er 40 is identical in physical dimensions with the cylinder 2t) and is provided with' a plugl 4i at one' end (which corresponds' with the plug 21) and the plug 42 at the other Aend (which corresponds with the plug 22). However, the plug 42 does not have a connection such as at 13 but is merely' provided with` a vent hole' at 43; Electricall connections are made via line 26' to junction 45 and thence through resistor 46 to' junction 47 and then through battery 48 and line 49 to junction 5G, from which a connec'zti'o'i'ry is made' back to junction 25. From junction Sil a connection is' also m'a'de to junction 51 on that end'of cylinder 40' which is vadjacent the' plug 4l. From junction 47 a circuit` extends through the resistor 52 to junction 53 and thence to terminal 54 on the Opf- Vposite end of cylinder 49. Agalvano'm'eter 55 is 9011- nected across junctions 45 and 53. When pressure is ap-J plied via arrow 56 throughv pipe 13 to the interior of cylinder 20, the eylinder'ZO will be placed under stress and the resistance between terminals 24 and 25y will" be changed'. At the same time th'e resistance' between te'rI rninals 51 and 54 on'` the tube 40 will not be changed',- since the 'tube' 4d is not under stress; However, since tube 20 and tube 40 are within close proximity of each' other, and' are accordingly subjectedtothe' same temperature', resistance changes due to temperature'. changes will be cancelled out duef to' the circuit network that'is shown, and the net effect will' be to provide al reading across galvauorneter 55 which is an indication of the pressure applied to the cylinder 20.

In FIGURE 5 there is illustrated` al modied form of the invention similar to FIGURE 4 in which cylinders" Ztl and 40 are identical with those shown in FIGURE 4, with the' singley exception that the' plug' 42 of FIGURE' 4 is yprovided with an aperture 43, whereas the corresponding plug 42A of FIGURE 5 is solid and is not provided with an aperture, and accordingly the tube 40 together with the plugs 41 and 42A form a sealed container similar to that Yshown in' FIGURE 3. In FIGURE 5 there is provided a container 35 similar to that described with reference to FIGURE 3. In this system the' pipe I3 which `connects through plug 2.2'l to the cylinder 2u is provided with a T at 13A to which the line 360i the cylinder' 35 is connected, so that when pressure isapplied via arrow 56 to line 13 this pressure will not only be applied on the interior ofthetube Ztl but will also beappliedl through line 36 to the container 35 and hence to. the exterior otl the sealed tube liti. The circuitry connections shown in FIGURE are the same as in FGURE 4 and therefore eed not be specifically described.

Accordingly, when pressure is applied via arrow 56 to the pipe i3, the pressure is introduced into the interior of the tube 2b thereby stressing this tube from the interior and it is applied to the exterior of the tube di) thereby stressing it in the opposite direction, i.e. from the exterior. These stresses cause resistivity changes of opposite character which, through the circuitry illustrated in FlGURE 5, provide a greater signal at galvanometer 55 than is supplied in FIGURE 4.

ln FGURE 6 a system is illustrated which is similar to that shown in EGURE 4 execpt that in the place of short, relatively lareg diameter tubes 12o and Atti as shown in FIGURE 4, in FIGURE 6 there is provided a long length of small diameter capillary tube generally designated under the bracket ci), and composed of equal portions iiA and 66B. Tris capillary tube is of uniform diameter and at one end of section nti/ there is provided an enlarged pressure connection til, and a terminal 2d similar to FIGURE 4. This length of capillary tube 6@ is of uniform diameter throughout its length and at the midpoint of the tube it is sealed shut at 63C and is provided with a terminal at the point 5d, which electrically serves parts odA and tB. The opposite end of part 66B of the tube is open at d?. and is provided with an electrical terminal at 54, simiiar to FIGURE 4. it is noted that the portion of the tube from the inlet connection 61 to the seal titi@ provides a sealed chamber of capillary dimensions equal to one-half the total length of the tube dit from the terminal 2d to the terminal 5d whereas that portion of the tube edi-3 from the seal 69C and terminal Sti to the open end 62 and terminal is likewise a chamber of capiliary dimensions which is equal in length to that from 2.4 to @dC but with this difference: it is open to the atmosphere at 62..

The circuitry for this form of the invention is identical with that shown in FGURE 4 and therefore need not be further described.

Accordingly, when pressure is applied by way of arrow 5d through iniet connection 61, the portion of the capiilary tube from the inlet to the seal-off at 66C, will be placed under stress, whereas that portion of the tube from t@ to d2 will not be so stressed but it is or" the same physical dimensions and subject to the same temperature as is the portion from 6i to o7.. The net result is that, with the circuitry shown, a signal will be provided at galvanometer 55' which is an indication of the pressure applied via arrow 56 to the iniet connection 6i. The capillary tube formed as shown in FGURE 6 has special applicability in many places where a small diameter tube can be accommodated to other mechanical structures.

FGURE 7 is the same as FEGURE 6 except that the capillary tube is folded at the seal Sti-C and terminal Sti, and the open end o2 is brought back to adjacent the inlet pipe nl, or the structure can be composed of two pieces of capillary tube which aro seaied together and sealed oi at @JC and provided with terminal So. The two sections of capillary tubing thus extending alongside of each other may, if desired, be formed into a spiral as indicated under the bracket et?, see EGURE 7, tie spiral in this case being composed of the two portions @QA and dit@ of the tube which lie parallel to each other separated by appropriate electrical insulation and are spiralled together. This form of mechanical construction perfectly accommo dates itself to attachment of the double spiral configuration to any central mechanical support.

The functioning of the device is electrically the same as that shown in FEGURE 6.

In EiGUP-E 8, two tubes 95 and 9d are provided, each of which supplies a change in resistance when pressure is applied. The tube h5 is provided with plugs 97 at one end through which an inlet pipe 9E extends. The pipe 98 and plug 97 are hermetically sealed to each other and to the tube 95.

At the other end of the tube there is provided a plug 99 through which the tube 96 extends, the tube 96 ybeing hermetically sealed to the plug 99 and the plug 99 sealed to the tube QS. The end 96A of the tube 95 is fur nished with a plug 96B so that it is sealed at this end. Electrical connections are provided at each end of each of the tubes 95 and 96 as shown. Thus a circuit extends from terminal Etti 0n tube 95 through line 5.62 to junction ti and thence through line idd to battery 10S and through line Mio to junction iti?. From junction 167 a circuit extends through resistor Mitt to junction 1&9 and then via line lib to terminai iii on the opposite end of tube 95'. From terminal M2 on one end of tube 96 a circuit'extends via line 113 to junction 93. From the other end of tube 96 a circuit extends from terminal iid through line its' to junction iid from which a circuit extends back through resistor M7 to junction E67. A galvanometer lid is connected between junctions lb? and H6. Pressure tight insulators are provided at H3A and iitb'A where lines M3 and M5 respectively pass through the Wall of tube 95.

in FiGURE 9 there is illustrated another form of the invention wherein the tubes, corresponding to tubes 96 and $5 are made integral, such forms of construction being especially adapted where the material of which the device is constructed is of a semi-conductor such as germanium or silicon or semi-conductor compound such as silicon carbide. ln FiGUiE 9 there is a unitary structure having a base 12b and an annular ange (or cylinder) at mi which, with the base, forms a cup shane. Within the annular flange (cylinder 12D there is co-axially formed a smaller inner annular flange (or cylinder) 122. These two flanges mi and 122 are concentric and extend to the left from the base titi, as shown in FIGURE 9, and are such that they terminate at approximately equal distances from the base 12b. The two iianges thus form a space fd between them, and this space is sealed by means of an annular glass seal 125 which is fused to the iianges ill and i212 so as to form a hermetic seal therewith. The glass seal 3125, at one place, is provided with a tube iii/o which extends through the seal into the space i224, so as to communicate therewith. The tube 25 is connected to a source of pressure as indicated by arrow 127, so that liuid under pressure is introduced into the space E24 which therefore stresses each of the cylinders E22 and E21 of the device. Connections are provided at i255 and 29 and i3d as shown. The wiring for the device shown in HGURE S? can be the same as in FiGURE 8, thus the connection i3@ may be connected to line ldd of the circuitry shown in FIGURE 8 and the connections 12S and 129 are connected respectively to the lines Mii and it of the circuitry shown in FGURE 8 One or both of the circuit resistors 46 and 52 of FIGURES 4, 5, 6 and 7, and circuit resistors 117 and 103 of FiGURE 8, can be made variable if desired for convenience in adjustment.

In FIGURES 2 9, the electrical terminals are illustrated as at the ends of the transducer elements, but it is to be understood that these terminals or additional terminals may be placed short of the ends, or at intermediate locations where other or different voltages or portions of voltages are desired to be read oit. This is particularly true in respect to transducers composed of semi-conductors wherein the orientation of the crystal planes of the semi-conductor material has an effect on the places where maximum transducive effect will appear.

Therefore, it is within the purview of the invention to locate the electrical terminals on any separated places on the element for obtaining the optimum signal effect.

Referring to FGURE 10, the pressure transducer device is a vessel which can, conveniently, be in the form of a hemisphere 2lb or any other cup-shaped container, having an edge or rim 211. Upon this edge or eerdere rim wh-ich'can be flat, there is fastened a circular disc 212 which is sol-dered, brazed, or otherwise fastened in pressure tight relationship to the edge surface 211 of the container 210. The disc is made thin relative to its diameter so that membrane forces predominate under pressure load-ing. The container has a pressure inlet connection 214 which communicates with the interior thereof. A smallslug 215 of metal forming an electric terminal is fastened to the center of the disc 212 and an electrical connection 216 is attached to the container 21@ which, if it is metalli-c, acts as a terminal. When cup 210 is nonmetallic, a separate ring terminal is supplied as at 2119A and 241 of FIGURE 12. Lead wire 217 extends from terminal 215 to one terminal 213 of the bridge circuit generally designated 220. Lead wire 219 extends from terminal 215 to terminal 221 of the bridge network 220. The bridge network 22? contains terminals 222 and 223. A battery 224 is vconnected across terminals 21S and 223 'and a galvanorneter 22S is connected across terminals 221 and 222. A resistor 226 is connected between terminals 218 and 222, resistor 227 is connected between terminals 222 and 223; and resistor 223 is connected between terminals 221 and 223. Resistances 226, 227 and 228, or some of them, may be adjustable if desired.

When pressure is applied via pipe 14 to the interior of the vessel 21th, the pressure generated therein will cause the circular membrane 212 to be deflected from its planar condition. lf the pressure applied to pipe 214 is a positive pressure the membrane 212 will be flexed outwardly Y(or to the right) as shown in FIGURE l0. It a negative pressure is applied to pipe 214, the disc 212 will be iiexed inwardly (or to the left) as shown in FIGURE l0. Flexure in either direction causes, thel material of which the disc 212 is composed to be stressed and this causes a change in resistance to occur between the center terminal 215 and the rim terminal 216, which change in resistance is reflected as a signal that actuates the gal vanometer 225 of the output circuit. Accordingly, the signal is shown directly by a member which is a part of the pressure system upon which the pressure is applied.

FIGURE l1 is a similar to FIGURE l() except that the container 21@ is not provided with an inlet pip-e 214 and `the container 210 is sealed oit by the circular disc 212. The entire closed vessel 21d- 212 is placed within a pressure tight receptacle generally designated 238 which has a liuid pressure inlet pipe at 231. The lead wires 217 and 219 are taken out through the walls of a pressure container 3i) through suitable pressure tight insulators 217A and 219A lin the wall. The external circuitry is identical with that shown in FIGURE l0.

Accordingly, when a pressure is applied to pipe 231 the circular membrane 212 will be deflected and stressed, and its resistance accordingly changed, which will be re- Y tlected as a signal at the read-out circuit.

yIn FIGURE l2 there is illustrated another form of the invention wherein a pair of membranes 24) and 2111 of identical type are sealed in pressure tight relationship to a ring 242 of insulating material such as ceramic `material. Each of the membranes 240 and 241 is provided with a terminal ring as at 240A and 241A and a central terminal as at 240B and 241B. The entire capsule, thus composed of the discs 241) and 241 which are attached in pressure tight vrelationship to the electrically non-conductive ring 242, is placed within a pressure container 44, which has an inlet 2415. The pressure container is provided with insulators at 2451-249. A circuit extends frem the battery 25d via line251 to terminal i 252 and thence via line 253 to the terminal 241B. From terminal 25?. thecircuitextends via line 254 and resistor 255 to junction 256 and thence vialine r2.57 to terminal 245B. From junction 256 a circuit extends via line 258 through galvanometer 259 to junctionV 25d; a circuit also extends through resistor 262 to junction 253 and thence via line 254 to terminal 240A. From junction 253 a 3 circuit also extends via line 265 to the opposite terminal of the battery 25d from the line 251.

When pressure is applied in the direction of arrow 26) to inlet pipe 245, the membranes 240 and 241 will be deflected inwardly thereby being stressed. This provid-es a change of resistivity, which is relected as an output signal which is read on the galvanometer 259. It

will be noted that in this system the two discs24tt and t 241 constitute two legs of a bridge network, of which the other legs are composed of the resistors 255 and 262. Accordingly, there is a double signal generated byv-this arrangement, as compared to the arrangement in FIG- URES 10 and 11.

Referring to FIGURE 13, there is illustrated another form of the invention which is composed ot' a disc 271) of metal, which is attached in pressure tight relation to the rim of a hemisphere 271. This can be most con- -veni'ently accomplished by brazing, welding or soldering Vtery 278. The circuit then continues via line 279 to junction 280 of the bridge circuit and via line 281 to the terminal 271A. From junction 276 of the bridge network, acircuit extends via resistor 282 to junction 283 and thence via resistor 284 to junction 28d. The galvanometer 285 is connected across the junction 273 and 283 of the bridge network. j

The disc 270 is provided with an inlet pipe 286 which communicates with the interior of the vessel which is formed by the disc 270 and the hemisphere 271. Accordingly, when pressure is applied via the pipe 286, as shown by the arrow 237, a pressure is communicated to the interior of the vessel 270-271, thereby imposing al stress upon the hemisphere 271, which therefore changes its resistance between the terminals 270A and 271A. This change in resistance constitutes a signal which is read by means of the rgalvanometer in the bridge network 274.

Referring to FIGURE 14, there is illustrated another form of the invention wherein two hemispheres are nested into the structure generally designated 2919. The axis of this structure is along the line 293 and intersects the hemispheres at its poles 297 and 298. The hemispheres 291 and 292 join at the ring 295. In vorder to make a tight junction between the hemispheres 221 and 292, and the ring `29115, rthe latter is preferably provided with two grooves 295A and` 295B into which the edges of the hernispheres are itted and then soldered or ybrazed in place. Ring 295 is thus a fluid tight closure between the hemispheres 291 and 292 land actsV as an electrical terminal to said edges.v The ring 295 forms an electrical terminal which is located in a plane at right angles to the axis 253, and (electrically) midway between the poles 297 and 2% of the hemispheres.V At Vthe poles 297 and 295 of the hemispheres, there are fastened terminals y 292A and 221A respectively. Thus, for the hemisphere 291 there is provided a polar terminal 291A and for the hemisphere 292 of the sphere there is provided a polar terminal 2912A. The terminal 292A is apertured to receive a pressure pipe 299 which communicates with the interior space S between the two hemispheres. From terminal 221A a circuit extends via line 351B' -to junction of arrow l sion. These stresses change the resistances of each ol the heinispheres Edil and flits?, and accordingly the resistance of the hemisphere 2%, as read between the polar terminal and the equator` terminal 295 will change a certain amount. Similarly, the resistance of the hemisphere 292 as read between the polar terminal ZA and the equator terminal 295 will likewise chance the same amount. However, these changes in resistance produce opposite eifccts in the bridge network into which they are connected, and therefore produce approximately double the signal as provided in FlGURE 13.

Referring to FlGURE there is illustrated ano-ther forrn of the invention wherein the pressure vessel 32h is provided with an inlet B2i and an opening dehned by the ferrule Within the fcrrule there is Fixedly at- -tached the thick rirn 3233 of a semi-conductor disc 322, which is made integral with the rim 323. Terminals are placed on the disc portion 3ft-2 as at 32e-227 and 323 as shown in FGURIE 16.

lt is often desirable, when using a semi-conductor pressure transducer element that the surface o the semiconductor is treated so that it is impregnated with or combined with an element which changes the electrical resistance of the portion which is so treated. This is known as doping Thus, the arcuate section extending troni the center terminal 32o and extending outwardly beyond the terminal 32S, includes the portions A and B. This entire arcuate or pie-shaped section may be treated by doping the original surface or the serniconductive disc 323 with a material which is foreign to the semi-conductor rnate ial, and which, when combined with it, produces a compound or impurity relationship that reduces the resistivity throughout the treated section. As an example, the semi-conductor may be composed of silicon, indium-antemcnide or germanium. lt has been found, in the present invention, that a senti-conductor pressure transducer element which has a portion or its surface doped, will in many instances, have improved signal output under the conditions ot stress that occur in the pressure transducer elements.

For example, the disc 322 may be composed of high purity Ntype silicon exhi iting a resistivity in t .e order of LUM-4,000 ohms per centimeter. A relatively heavy coat of silicon dioxide is then grown on the surface of the disc by subjecting it to oxidizing atmosphere at elevated temperatures. This oxide coating is then etched oit throughout the rea of the segment desired to be doped, which as shown in FGURE 16 is the pie-shaped segment including the area of terminals outwardly beyond the terminal 32S. Then the semi-condoctor elernen `with the oxide coating etched away in the desired to be doped is subjected to an arse ic atmosphere at Van elevated temperature. rthe arsenic eadily diffuses into the silicon but diffuses at a much slower rate through the protective coating of silicon dioxide. After the dir'iusion has proceeded to a selected vtor exai ple to a depth oi .080i inch-.Q05 inch, the treatment is stopped and the disc is then d and aged. 'thereafter the electrical contacts 7 32? are attached at thepositions shown.

on process can oe regulated in regards to time, temperature, and the quantity and type of doping matera, so as to achieve a thickness and resistivity throughout the pie-shaped segment in the order of 1 oh1ncentimeter. The selection of the area for doping can be predetermined beforehand and by known techniques, by examining the semi-conductor (or cutting it) accordingr to a definite pattern with reference to its crystallization planes, or the areas selected tor doping. can be seand usi lected by experiment, merely by doping several areas, more than needed, and providing each area with terminals. Substantially all of the doped areas will produce some signal when the transducer is pressure stressed and measurements taken ot the amount or signal response will sho-w which areas produce the optimum signals. Thus, more doped areas than needed, variously oriented, would be made, and the best selected. This is an empirical selection.

The base material, here illustrated as the original silicon acts essentially as an insulator in the presence of the low resistivity doped segments. In some cases one may use an Ntype doping material on a Ptype base material, and this results in a rectifying contact at the interface of the two materials. rl`his rectifying action enhances the insulating properties of the base material.

The doping of a selected area of the semi-conductor material may also be accomplished by plating on or vacuum depositing a thin layer of the doping material over the region which is desired to be treated, and then carrying on the ditusion of the doping material at an elevated temperature, and thereafter annealing and aging the unit, after which the electrical contacts are applied as previously described.

in the illustration FiGURE-S l5 16, electrical circuits are connected to the three terminals and when pressure is applied to the connection 32?., the disc will be flexed, thereby causing the thin layer of material in the areas A and B, see FlG-Ull 16, to be stressed so that one area is in tension and the other is in compression, and when this occurs, the electrical resistance between the terminals 326 and 327 and between the terminals 327 and 3153 will change, but not in the saine amount or order. By appropriate instrun'ientation, the changing electrical signals thus derived may be calibrated in terms of pressure applied to the inlet 323i.

in FlGUiES l5 and 16 the disc element 22, being ysupported xedly by the heavy rim 323 pro-vides a reversal of liexure between the rim E323 and the center. This provides a diversity of signal as between the contacts 32dand the contacts 327-32dln the forni of invention shown in FlGURES 17 and 18, the transducer element is a disc 335 which is supported by the tree edge supports 1 3dr-334, which are the forni of O-rin s that are 1 lightly cramped in the errule 3.s2d32A-332B. When een is applied to the container this d es not hold the edge of the disc against ending The (bring ses is only lightly hel-d against the surface 335 and does not measurably restrict the iiexing of the disc produced by pressure against it.

As shown in FGURES 18 and i9, the `surface of the disc 335 may be doped according to varying patterns. ln FYGUEE l there are two pie-shaped segments CD ema- .l hating rom the center terminal 33d and ending respectively at the terminals 338 'and 337. These pie-shaped segments are doped, by treating the initial-ly pure semiconductor material by impregnating it and/or reacting it with a compound which, in association with pure semiconductor material, will produce a lowering of the resistance ras compared tothe resistance of the pure material. Thus, in these areas C and D the treatment is as previously describe-d, and these areas are relatively rnucn more conductive than the original semi-conductor material of which the disc 335 is composed. The lead wires 339 are connected to the terminals 335-333 and when pressure is `applied to the disc, causing it to flex, the resistance between terminals 336 and 337 will change and the resistance between terminals 33o and 333 will likewise change, but in opposite sign. Accordingly, such signal may be used in an appropriate bridge circuit, of the type 1 1 previously described herein, for indicating the pressure applied to the inlet 331.

As shown in FIGURE 19, the area of the semi-conductor material which is doped need not be a pie-shaped area emanating from the center of the disc, but one or several random disposed areas E on the same dis-c may be utilized. A larger number of such areas than will be used may be doped and one or more of them selected by measurement or use, as previously described. The random disposition of the arcas results because the crystal structure o the semiconductor material, from which the disc is cut, will exhibit ditierent resistivities, according to the relationship of the plane of the disc to the crystallographic planes of the original material. rl`he optimum orientation of the plane of cut and of the area (areas) selected for doping for producing a unit of optimum response can be predetermined before cutting and doping by long and complicated calculations, and this method may be used but reasonably good and useful results c-an be determined empirically by experimentation, as described, for producing a useful product. These general rules apply to all, coniigurations .of semi-conductor transducers made according to the present invention.

Thus, in FIGURE 19 an area E is doped, and provided with terminals 341 and 342, which are connected to the external circuit 343 for reading the signal.

FIGURE 20 illustrates a form of disc coniiguration composed of semi-conductor material which will exhibit substantially a free edge support for the eiiective central area of the disc, and yet allow la soiid clamping of the rim of the transducer. Thus, the disc 25u is provided with concentric grooves 31 and 352 at slightly different radii and of suicient depth so as to leave between them a flange 351i of the original material, which serves .to attach the rim portion 357 to the central portion of the disc. This flange is sufciently thin so as to accept the dexure caused by pressure being applied to the disc in the direction of arrow 355 or 3556, but will not so support the edge of the central portion of the disc as to prevent it from flexing as a free edge supporting disc. The doped areas on the central portion are selected and produced as previously described.

FIGURE 2l illustrates a form of tubular transducer 2-60 composed of semi-conductor material and illustrates that the doped areas of such semi-conductor material may be randomly disposed. Thus, for example, the area K and L, which are formed by treatment as previously described, are predetermined mathematically or selected byy experiment so as to exhibit the optimum change or" resistance for a given change of pressure applied to theA tubular structure. Each of' the areas is provided with terminals, thus area I( being provided with terminals 351 and 362 whereas area I. is provided with terminal-s 3dr-fl andl 365. These mayv be utilized as legs or the same bridge circuit for reading the output signal, which may,` be calibrated in terms of pressure applied to the inside or outside of the tube as sho-wn in FIGURES 2, 3, etc.

In any of the bridge circuits herein described one or more of the bridge reslstanccs may be mede variable for purposes of adjustment. It is usually preferable to adjust the bridge circuit -to give a zero deflection of the galvanometer under conditions` of no stress on the transducer elements, and to calibrate the galvano-meter (or one resistor) in terms of pressure applied to the transducer iluid inlet.

In the embodiments of the invention illustrated in FIP- URES 2.229 and described hereinafter, a constant current is passed through a semi-conductor and the output voltage perpendicular to the ilow of current resulting from the application of a iiuid pressure producing a force stressing the semi-conductor is measured. By locating the terminals at which vthe voltage measurement is taken in spaced relation relative to the terminals at which a current is applied to the semi-conductor perpendicular to the ilow` ofA current, and spaced from each other nov volt- -age signal is produced when the semi-conductor is in an unstressed condition. However by applying a stress by introducing iiuid under pressure into a container on which the semi-conductor is located or a container that at least in part is formed by the semi-conductor, the semi-conductor is stressed and thereby a measurement of the pre-ssure` applied may be obtained by using apparatus of the nature described hereinafter since the voltage obtained is a function of the stress in the system and the current perpendicular to the measured voltage.

In FIGURES 22-24, the integral strain transducer illustrated is a container @dit which is of a construction similar to container 20 of FIGURE l. The container dit@ is made up of a tube 4h31 of a semi-conductive material such as silicon and at either end plugs im and 405 are sealed to the tube. The plug 4112, is apertured so as to receive the pipe 404, by means or which a fluid pressure may be introduced into the container.

A ring terminal (conductive electrode) lilo is secured to one end face of the tube concentric to the longitudinal axis of the tube while a second ringterminal 497 is likewise secured to the opposite end face of the tube. A lead Wire dhd extends from terminal #15W to one terminal of an appropriate voltage measuring device 409. A second terminal of device 4439 is connected to terminal dilo by lead wire 411B.

A third ring terminal (conductive electrode) 411 is secured to the inner peripheral wall of the tube 101 while a fourth ring terminal i12 is secured to the outer peripheral wall concentric to the third terminal. Preferably the ring terminals fiile, 46S, 111 and 412 are made of a material such as nickel. The terminals are symmetrically located. Also the terminals 4de and 11% are located to measure the voltage perpendicular to the flow of current between terminals 411 and 412.

In order to produce a iiow of current between the last mentioned terminals, a variable resistor 414 is connected across junction 415 and terminal 412, while battery 416 is connected across junctions 415 and 417. An ammeter 418 is connected across junctions 417 and terminal 411, the lead wire 419 connecting the ammeter to terminal 411 being taken out through the wall of container throughV a pressure tight insulating bushing 420. By passing a constant current between terminals 411 and 412 when no iiuid pressureis applied through pipe 4114i, no voltage is indicated between terminals dile and 4117. However upon Vapplying pressure at pipe dhd the container dit@ is placed under stress and accordingly a voltage measurement indicative of the pressure is obtained at terminals dtl and 4117.

It is to be understood that the source of current may be applied across terminals 466 and 407, and that the voltage measurement taken across terminals 411 and 412 instead are described heretofore. Also the terminals 411 and 412 may be made to extend substantially the axial length of the tube intermediate plugs 4112 and 403, if desired.

Another embodiment of the invention utilizing a treated semi-conductor disc and generally designated 425 is in part illustrated in FIGURE 25. The disc 426 of the embodiment, generally designated 425, has a doped area 427 that is prepared in accordance with the principles set forth in the discussion of the embodiments of FIG- URES 15-19. The disc 426 having the doped area 127 is mounted to form part of a container such as the disc 212 of FIGURE 10 or FIGURE 12 or mounted on the container 32@ of FIGURE 15 or container 33d of FIG URE 17, it being understood that the disc 426 is made of a semi-conductive material. At one end of the doped area 427 there is provided a terminal 42S While at the opposite end there is provided a terminal 429. The terminals 428, 429 are connected, through lead wires 439 to circuitry such as illustrated in FIGURE 22 for applying current through said terminals. Y

Intermediate the terminals 42d and 429. and on one side ofA the doped areathere is provided a terminal 431 and iii on the opposite side there is a terminal 432. The terminals 431i and 432 are located to measure the voltage, ir" any, perpendicular to the flow of current through terminals 423 and $29, the aforementioned terminals being symmetrically located. Lead wires 434i connect terminals 431 and 432 to an appropriate device to measure the voltage at said terminals. Accordingly when no pressure is applied to disc e226 and a constant current is applied across terminals 42S and 429 no voltage is observed across terminals fil and 532, however, by applying a pressure to the container in which disc 427 is mounted or forms a part of, an indication on the device connected at such as set forth relative to embodiment fitto is obtained.

As shown in FIGURES 28 and 29 the use of a doped area on a semi-conductor may be located other than on a ilat surface. For example, the doped area iil of the embodiment 44rd of FIGURES 28 and 29 is formed on the hemisphere 442 that is made of a semi-conductive material, the thickness being greatly exaggerated in FIG- URE 28 for purposes of illustration. A circular disc idd is attached to the edge of the hemisphere in pressure tight relation therewith. A pipe 45 opens into the interior of the thus formed container similarly as that illustrated in EGURE l0. However it is to be understood that the container of embodiment lieti may be located Within an enclosed container such as illustrated in FlGURE ll and in this case there would not be provided a pipe 45 opening into container dell.

Terminals 446 are provided on the oppositely disposed sides of the area dei to applied current therethrough While terminals i457 are provided on the other pair of sides, each terminal being located as embodiment 1f-25. The voltage is measured across lead Wires d@ by a device in the manner described with reference to FlGURE 22, lead Wires Lidi being connected to terminals 44". A source of current is connected to lead wires 45o which in turn are connected to terminal 4de.

lt is to be understood that a disc i255 together With its circuitry as shown in lilGURE 25 may be substituted for the disc i44- of FIGURE 28. in such a case it is not necessary that the hemisphere 44,2 be made of a semiconductive material. Also it is to be understood that the embodiment 44d may also be modied by using a Serniconductive hemisphere Without a doped area del and a signal of the nature described heretofore will be produced through stressing the container, provided the terminals are connected to the hemisphere in spaced relationship such as illustrated in FlGURE 29.

Another embodiment of the invention, generally designated 475 and illustrated in ELGURES 26 and 27, comprises a hemisphere 47e of a semi-conductive material. A circular disc 1.177 is attached to the hemisphere to form a pressure tight seal with the edge 65A thereof. A pipe 47h opens through the disc to enable applying a pressure to the interior of the thus formed container.

A slug of metal forms a terminal 4?@ at the axis of the hemisphere. A ring terminal (conductive electrode titl is attached to the hemisphere concentric to said axis nd singularly spaced from terminal 6.,. Lead vites 8l connect the terminals 479, to an appropriate source of current such as describe relative to FIGURE 22.

A conductive ring termina.

is secured to the outer urface ot the hemisphere il o be concentric to the axis of the hemisphere, angularly spaced from terminals 47', and intermediate terminals 479, if A second ring terminal i3d is likewise attached to the hemisphere other than that it is attached to the inner peripheral wall thereof and it is located on a radius line that extends through the center of curvature C of the hemisphere and passes through terminal 533 whereby the terminals are located perpendicular to the flow of current.

laead Wire idd connects terminal 2.553 to one terminal of an appropriate Voltage measuring device such as described beretoore while lead Wire ille? is connected to the opposite erminal of said device. The lead wire 435 is extended through a pressure tight insulating bushing idd in the membrane 77 and connected to terminal 48d.. The lead Wires are connected to a source of constant current such as indicated in FIGURE 22. lt is believed the operation of embodiment 475' is apx arent from the description ot the various embodiments described hereto- Ifore and therefore will not be set forth.

it is to be understood that embodiment 47S may be modiied by providing a disc without a pipe located therein and mounted in an enclosed container such as container 23d of FGURE ll. 'in such a case the fluid pressure would exert a force on 'the exterior of the hemisphere rather than the interior. Appropriate pressure tight bushing would be provided in the outer container to have the respective lead wires extend to a current source and a voltage measuring device.

ln each one of the embodiments described heretofore, the container in an unstressed condition has a wall portion of a given electrical conduction characteristic. However upon stressing said Wall portion, said electrical conduction characteristic is changed and a measurement of this change gives an indication of the liuid pressure that the container is subjected to that brings about the stressed condition.

This application is a continuation-in-part of my applications Serial Nos. 22,186 and 22,187, bothL tiled April 14, 1960.

As many widely apparently different embodiments of this invention may be made Without departing from the spirit and scope thereof, it is to be understood that l do `not limit myself to the specific embodiments herein.

What l claim is:

l. An integral strain transducer comprising a pressuretight container constructed so as to be capable of being subjected to pressure, said container including a Wall portion which is stressed when the container is subjected to pressure and which is composed of a material capable of changing its electrical resistance between spaced locations thereon when so stressed, and separate electrical terminals solidly affixed electrically and mechanically at said spaced locations, said terminals being of a character such that the area of contact between the terminal and the container will ren :in substantially constant.

2. The transducer specilied in claim l further characterizcd in tha said wall portion is composed of a semiconductor having a certain resistance between said terminals when the semi-conductor is not stressed and a ditrerent resistance between said terminals when the semiconductor' is stresser.

3. The transducer specied in claim l further characteiired. in that said wall portion is composed of a material having a prescribed electrical resistance generally, a portion or tne said wall of different purity, said electric terminals being at spaced locations on said portion.

4. The transducer of claim l further characterized in wall portion is a cylinder of semi-conductor 5. lire transducer of claim l further characterized in that Wall portion is a membrane of semi-conductor said Wall portion is composed of a semi-conductor of a ertain purity and electrical resistivity, a segment of the area. of said semi-conductor being rendered less pure envases byY introducing therein a material which lowers the resistance of the semi-conductor material, said segment being a shallow layer on said semi-conductor, said electrical terminals being located along said segment.

9. The transducer of claim 8 further characterized in that more than two electrical terminals are provided at spaced locations along said segment.

1G. The transducer of claim l further characterized in that said wall portion is composed of a semi-conductor of a certain purity and electrical resistivity and several segments oi the semi-conductor are rendered less pure by introducing therein a material which lowers the resistance of the semi-conductor material and each segment, each segment being a shallow layer on said semi-conductor and each segment is provided with spaced electrical terminals thereon.

l1. The transducer specified in claim 8 further characterized in that said segment is located in respect to the crystallographic planes of the semi-conductor so as to provide optimum change in resistivity between said electrical terminals when the transducer is subjected to pressure.

12. The transducer of claim 1 further characterized in that said wall portion is composed of a semi-conductor of a certain purity and electrical resistivity and a segment of the area `of said semi-conductor is rendered less pure by introducing therein a material which lowers the resistance of the semi-conductor material, said seg-ment being a shallow layer on said semi-conductor, said material introduced into the semi-conductor being selected so as to provide a rectifying interface between the shallow layer and the semi-conductor contiguous thereto, said electrical terminals being located along said segment.

13. The transducer of claim l further characterized in that said wall portion is com-posed of a semi-conductor of a certain purity and electrical resistivity, at least two segments `on the surface of said semi-conductor being rendered less pure by introducing therein a material which lowers the resistance of the semi-conductor in said segments, said segments being shallow layers on said semiconductor, electrical terminals located at spaced positions on said segments, said segments being located at Y positions on the surface of said semi-conductor so that the stress produced in the semi-conductor when pressure is applied will cause a change of resistance ybetween the terminals of one segment which is opposite in sign to the change in resistance simultaneously produced between Ithe terminals of another segment.

14. An integral strain transducer comprising a tubular member `of electrically conductive material, at least one end of said tubular member being sealed, electrical terminals at two places along said tubular member, said places being axially spaced along said tubular member, said terminals being of iiXed area and solidly attached to the tubular member, and a pressure means connected to said tubular member for applying a iiuid pressure to the Walls of said tubular member.

l5. rThe apparatus of claim 14 further characterized in that the pressure means communicates with the interior of said tubular member for applying fluid pressure to the interior of said member.

16. The apparatus of claim 14 further characterized in that said tubular member is sealed at both ends, and said pressure means includes a container in which the tubular member 4is positioned and in which pressure may be established.

17. An yintegral strain transducer system comprising first and second tubular .members of electrically conductive material, the lirst of which is closed for establishing `a pressure therein, pressure means connected to said irst tubular member for imposing a pressure on the walls of said tubular member, and electrical terminals at spaced places on each of said tubular members, said terminals 'being of iixed area and solidly attached to the tubular member.

18. The system of claim 17 further characterized in that said iirst and second `tubular members are separate tubes and said pressure means is connected to at least one of said tubes for imposing a pressure thereon.

19. The system of claim 17 further characterized in that said first and second'tubular members are composed of irst and second lengths oi capillary tubing having adjacent ends sealed and connected together, the opposite end of the iirst length of tubing being connected to said pressure means, and the opposite end of the second length of tubing being open and electrical connections at said .opposite ends of each length of tubing and where said lengths of tubing are connected.

20. The system of claim 19 further characterized in that said first and second tubular members are nested one inside the other.

2l. An integral strain transducer comprising a tubular member sealed at opposite ends, electrical terminals of fixed area solidly attached at spaced places on said tubular flmember, said transducer ybeing composed of manganin.

2,2. An integral strain transducer comprising a tubular member sealed at opposite ends, electrical terminals of fixed area solidly attached at spaced places on said tubular member, said-transducer being composed of a semiconductor.

23. An integral strain transducer comprising an cuter cylindrical tube and an inner cylindrical member of smaller diameter nested together with the inner cylindrical member inside the outer cylindrical tube so as to provide an annular space between them, seal means closing the ends of saidannular space so as to form a pressure Itight space therebetween, a pressure connection into said space, and electrical terminals on the outer cylindrical tube said electrical terminals being of iixed area and solidly attached to said tube.

24. The transducer of claim 23 further characterized in that the outer cylindrical tube is integral with the inner cylindrical member at one end.

25. The transducer of claim 23 further characterized in that the outer cylindrical tube and inner cylindrical member are integral at one end and are composed of semi-conductor material.

26. An integral strain transducer comprising a pressuretight container constructed so as to be capable of being subjected to pressure, said container including a wall portion which is stressed when the container is subjected to pressure and which changes its electrical characteristics when stressed, iirst electrical terminals of constant area iixedly attached to said Wall portion, said first terminals being adapted to be connected to a source of electricity to provide a current ow in said wallportion, second terminals of constant area tixedly connected to said wall portion in spaced relation to the iirst terminals.

27. The transducer of claim 26 further characterized in that said terminals are located along a certain line, that the second terminals are located on a line at to the ilow of current in the direction of said certain line and that with no stress applied to the container and a current oW condition, the potential between the second terminals is of a prescribed value.

28. The transducer of claim 26 further characterized in that said wall portion is a cylinder of semi-conductor material.

29. The transducer of claim 26 further charac erized in that said wall portion is composed of la semi-conductor having a treated area to change the electrical characteristics thereof and said terminals are located in .said treated area.

30. An integral `strain transducer comprising a circular closure member Iof thin electrically conductive material forming at least one wall of la pressure vessel to which said closure member is attached in pre sure sealed relationship, said circular closure member being composed oi a material which changes its electrical resistance when it is stressed, electrical terminal means at spaced locations on the circular closure member, said terminals being solidly aiiixed mechanically and electrically on said Iclosure member, said terminals being of a character such that the area of contact of the terminal and the closure member remains constant, and pressure means connected to the pressure vessel for applying pressure thereto for thereby stressing the circular closure member.

31. rThe apparatus of claim 30 further characterized in that the circular closure member is a disc.

32. The apparatus of claim 30 further characterized in that the circular closure member is spherical.

33. The apparatus of cla-im 30 further characterized in that the pressure means comprises a pressure connection communicating with the interior of the pressure vessel.

34. The apparatus of claim 30 further characterized in that the circular closure member is of mangann.

35. An integral strain transducer assembly comprising a pair of discs of electrically conductive material fastened in pressure-tight relationship to opposite edges of a ring of electrically non-conductive material, terminal means around the periphery of cach disc and at the center of each disc and pressure means connected to the disc and ring `assembly for Iimposing a iiuid pressure thereon for stressing the discs.

36. An integral strain transducer assembly comprising a pair of thin circular electrical conductive elements arranged coaxially and spaced relative to each other, and with their circular peripheries proximate, an electrical terminal connected to the peripheries of said elements so as mechanically to join such peripheries in sealed relationship and to constitute an electrical term-inal common to said peripheries, `an electrical terminal attached to each element at its axis and a pressure connection through said assembly into the sealed space between said elements.

37. The assembly `of claim 36 further characterized in that the circular elements are hemispheres, one nested Within the other in spaced relationship.

References Cited in the file of this patent UNITED STATES PATENTS 1,896,193 Corson Feb. 7, 1933 2,365,015 Simmons Dec. 12, 1944 2,398,372 Green Apr. 16, 1946 2,421,907 lPostlewaite June 10, 1947 2,472,045 Gibbons May 3l, 1949 2,745,284 Fitzgerald et al. May 15, 1956 2,872,812 .Tones et a1. Feb. 10, 1959 FOREIGN PATENTS 1,177,677 France Apr. 28, 1959 

1. AN INTEGRAL STRAIN TRANSDUCER COMPRISING A PRESSURETIGHT CONTAINER CONSTRUCTED SO AS TO BE CAPABLE OF BEING SUBJECTED TO PRESSURE, SAID CONTAINER INCLUDING A WALL PORTION WHICH IS STRESSED WHEN THE CONTAINER IS SUBJECTED TO PRESSURE AND WHICH IS COMPOSED OF A MATERIAL CAPABLE OF CHANGING ITS ELECTRICAL RESISTANCE BETWEEN SPACED LOCATIONS THEREON WHEN SO STRESSED, AND SEPARATED ELECTRICAL TERMINALS SOLIDLY AFFIXED ELECTRICALLY AND MECHANICALLY AT SAID SPACED LOCATIONS, SAID TERMINALS BEING OF A CHARACTER SUCH THAT THE AREA OF CONTACT BETWEEN THE TERMINAL AND THE CONTAINER WILL REMAIN SUBSTANTIALLY CONSTANT. 